There is good evidence that macrophages have an important role in tumor cell destruction in specifically sensitized animals and that tumor cell killing is related to events taking place at the macrophage-tumor cell interface. Recently we have shown with a new electron microscopic technique that peritoneal macrophages and ascites tumor cells are covered with a variably thick layer of cell coat material which lies external to the trilaminar unit membrane; this cell coat undergoes striking morphologic (and probably biochemical) alterations during the course of cell-mediated hypersensitivity reactions. We will evaluate the role of the macrophage and tumor cell coat material in tumor destruction, using a combined morphologic (ultrastructural), biochemical and immunologic approach. We will isolate, purify, chemically characterize, and compare the cell coats of normal macrophages, or immunologically activated macrophages, and of ascites tumor cells. Antibodies to each type of cell coat material will be prepared and their effects on macrophage/tumor cell function will be studied. We will also evaluate several mechanisms by which lymphokines may effect the cell coats of macrophages and tumor cells, and the role of the cell coat in cellular adherence.